DRILLING DATA RECORDING

Mobile Electronic Recording System and Drill-off Data Illustrating Its Use

WARREN B. BROOKS MEMBER AIME SOCONY MOBIL OIL CO., INC.

JAMES T. DEAN DALLAS, TEX. Downloaded from http://onepetro.org/JPT/article-pdf/15/01/11/2213667/spe-409-pa.pdf by guest on 24 September 2021 WILTON GRAVLEY

Abstract Several mechanical and electrical recording systems for drilling variables are now available for rental or purchase. A mobile electronic system has been developed for These systems record from one to six variables. Accuracy, recording drilling variables. Continuous records have been sensitivity, reliability and durability vary considera?ly o.n made, during field tests, of drilling rate, weight on bit, these units. The oscillographic system described m thiS rotary rate, torque, fluid pressure and pump rate. Addi­ paper was designed for improved accuracy and sensitivity. tion~iiy, intermittent recordings have heen made of strains and accelerations in various pieces of drilling-rig equip­ The subject recording equipment has many uses. One ment, and longitudinal, torsional and bending stresses in frequent application has been the obtai~ing."of accur.ate the drill pipe. Transducers are placed on the rig for moni­ drill-off data. In many instances the Lubmski- calculatIOn uring the variables. Cahles connect the transducers through method for drill-off data is sufficiently accurate, However, circuits to an oscillograph. The major electronic compo­ in cases where severe buckling occurs during the drill-off nents of the equipment are housed in a trailer for protec­ or where the wall thickness of the drill pipe has changed tion and portability. due to wear or corrosion, this method can lead to con­ The electronic recording system facilitates taking accu­ siderable error. The technique described in this paper, rate drill-off data in the field. Data are presented on seven utilizing the recording sys:~m, eliminates these inaccuracies. drill-offs taken in San Andres dolomite in Andrews County, Tex., at a depth of about 5,020 ft. In the test interval, Description of the Recording System drilling rate was proportional to weight on hit and to rotary rate raised to the 0.6 power. The mobile monitoring system is durable and versatile. It was designed for use in the field or in the laboratory. Introduction Signals from strain-gauge, p8tentiometric and tachometer­ generator type transducers can be recorded. The frequ~ncy In the drilling research work conducted by Socony response and sensitivity of the circuits used for the vanous Mobil Oil Co., Inc., emphasis has been placed on a study measurements can be varied over wide ranges. of the factors affecting drilling rate, both with conventional In fabricating the circuitry and components, simplicity and new drilling devices. The effects of several inter­ was emphasized. This minimizes electronic problems result­ related variables. have been studied. These include drilling ing from transportation over rough terrain. Normally, sig­ rate, weight on bit, rotary rate, drill-string torque, drilling­ nals are recorded without the use of amplifiers, During fluid pressure and pump rate. early field tests the apparatus was housed in a converted In early field tests standard drilling-rig equipment was seismic-recording truck. The system was later installed in used in obtaining data. Because of the encouraging results a house trailer. This instrument trailer is shown on the obtained in these tests, an oscillographic recording system lower right in Fig. I, together with the I Y2 -ton truck used was fabricated. This mobile electronic recording equipment to transport the trailer. Hidden by the trailer is a portable has been used successfully in the field and in the Socony 5-kw AC generator utilized for power. Mobil Field Research Laboratory for four years. In addi­ Fig. 2 is a block diagram of the transducers, recorder tion 10 the mentioned variables, strains and accelerations and control equipment. Each transducer is connected to in the drill string and in various rig components have the control circuitry by a shielded four-conductor cable. been recorded and analyzed on several occasions. One such application occurred during Project Mohole, Phase 1. Fig. 3 shows the electronic equipment mounted in the Longitudinal, torsional and bending strains in the drill trailer. The oscillograph recorder is located on the table string were recorded while drilling in about 11,700 ft of at the left. The left relay rack contains an intercom system, water at the Guadalupe Island site.' control circuits for the transducers and a power supply. The right relay rack contains AC monitoring meters, a DC Original manuscript received in Society of Engineers office voltmeter, an oscilloscope and a voltage regulator. Aug. 18. 1962. Revi,:;,ed manuscript received Dec. 6, 1962. Paper presented Recorde~ at 37th Annual Fall Meeting of SPE. Oct. 7-10, UJ62, in Los Angeles. lReferences givt:.:n at end of paper. The oscillograph recorder is a la-channel, general-

JA:\I'ARY, 1963 SPE 409 11 purpose type. * A mercury-vapor lamp of high intensity TABLE l-VARIABLES RECORDED ON A AND TYPES OF TRANSDUCERS USED is used as the light source for the galvanometers. The Variable Recorded Type of Transducer recording paper is sensitive to ultra-violet light and devel­ Drilling rote Potentiometer ops under ordinary lighting without the use of fluids or Hook load (weight on bit) Strain-gauge pressure cell or stroj,n-gauge sub Rotary rate Tachometer-generator a dark room. Therefore, the record can be observed imme­ Torque Strain-gauge pressure ceJl or strain-gauge sub Fluid pressure Strain-gouge pressure cell diately and continuously. The records are not permanent; Pump rate Tachometer-generator however, they do not fade for a few weeks under fluores­ cent lighting. Permanent records are made by photostating or fixing (with a chemical solution) the original records Transducers at a later date. The types of transducers utilized for the six conven­ The paper drive on the recorder has eight different tional drilling variables are shown in Table 1. All of the speeds in increments between 1 ft/hr and 2 ft/sec. This transducers are connected and placed in operation without versatility permits recording high-frequency signals in any interruption of rig operation, with the exception of detail, and also makes possible recording signals con­ the torque transducer. The installation of this equipment tinuously for long periods of time. requires about one-half hour downtime on the rig. The frequency response of each trace depends on the Drilling Rate type of galvanometer and corresponding control circuit The drilling-rate transducer senses the linear displace­ used. The galvanometers have frequency responses ranging ment of the drilling cable on a sheave of the crown block from 24 to 2,000 cycles/sec. Galvanometer sensitivity (usually the "fast" sheave). The movement of the drilling Downloaded from http://onepetro.org/JPT/article-pdf/15/01/11/2213667/spe-409-pa.pdf by guest on 24 September 2021 varies inversely with frequency response. During most tests line is proportional to the movement of the traveling low-frequency, high-sensitivity galvanometers have been block. The transducer includes a wheel approximately 9 in. used. in diameter that is held against the cable on a sheave. Keyed to the wheel is a potentiometer. Movement of the

"Heiland Model 906A Visicorder. cable on the sheave turns the wheel and the potentiom­ eter. The resistance change in the potentiometer is sensed by the control circuit and transmitted to the recorder. The signal recorded is proportional to displacement of the drilling line and the kelly. Since it is recorded vs time, the slope of the trace on the record is proportional to drilling rate or to other movement of the drill string. Hook Load (Weight on Bit) The hook load has been sensed by the following two methods. 1. Modified Commercial Unit-The hook load has been sensed by a strain-gauge type of pressure transducer in­ serted in a standard weight-indicator system. This standard system measures tension in the deadline (proportional to hook load) with a diaphragm unit on the deadline tie­ down. The diaphragm is connected to the weight-indicator gauge (a pressure gauge) by a liquid-filled line. A pressure transducer is connected to this line, thereby giving a signal proportional to hook load. Weight on bit is the difference between the hook-load values when the bit is just off­ bottom and Oil-bottom. 2. Strain Gauges Mounted on a Sub in the Drill String-The hook load (the reading is actually hook load Fig. I-Mobile electronic recording system on drilling rig.

DRILLING RATE

HOOK LOAD

ROTARY RATE

CONTROL TORQUE EQU IPMENT

FLUID PRESSURE

PUMP RATE

IOTHER VARIABLES r · Fig. 2---'Block diagram of recording equipment. Fig. 3-Recording equipment inside the instrument trailer.

12 JOURNAL OF PETROLEUM :rECH!'iOLOGY minus the weight of the kelly and swivel) has been sensed wheel of the torque unit. The speed of the idler wheel IS during some studies by a strain-gauge bridge mounted on proportional to the rotation rate of the rotary table. a sub placed immediately below the kelly. A cable attached to the bridge enters the interior of the sub through a Torque special seal, traverses the interior of the kelly and then Torque has been sensed by the following two methods. returns through a seal to the outside above the kelly. The 1. Modified Commercial Unit-One torque transducer cable is connected to a set of slip rings. A separate cable is a modified Martin-Decker Hydro-Mech unit. The device connected to the brushes on the rings transmits the signal consists of an idler wheel which is forced against the tight to the oscillograph. This system has greater accuracy and side of the rotary drive chain. The force on the idler wheel sensitivity, but less durability, than the unit described is proportional to the tension in the chain and, thus, to the earlier. torque at the rotary table. Force on the idler wheel devel­ ops a pressure proportional to torque in a fluid-filled Rotary Rate system containing a piston-cylinder that supports the wheel. A DC tachometer-generator for monitoring the speed Signals proportional to torque have been recorded by of the rotary table is mounted on the shaft of the "idler" sensing the pressure in the cylinder with a strain-gauge type of pressure transducer. 2. Strain Gauges Mounted on a Sub in the Drill String-The sub previously described also has a strain­ gauge bridge mounted in such a manner that torsion is monitored. A cable is connected to the oscillograph similar to the method described for hook load. Downloaded from http://onepetro.org/JPT/article-pdf/15/01/11/2213667/spe-409-pa.pdf by guest on 24 September 2021 Drilling-Fluid Pressure A strain-gauge type of pressure cell is used to monitor the pressure of the . It is connected to the stand pipe in an easily accessible place. Pump Rate The pump-rate transducer has a wheel about 9 in. in diameter which is held in contact with the pinion shaft of the pump (or some other rotating member of the pump). Keyed to the wheel is a DC tachometer-generator. Rotation of the pump shaft turns the wheel and tachometer. The signal generated is proportional to pump rate; it is sensed by the control circuit and transmitted to the recorder. Fig. 4 is a photograph of the pump-rate transducer in Fig. 4-Pump rate transducer. operation.

Fig. 5-0sciIlograph record coming out of hole.

JANUARY, 1963 13 Illustration of Signals Recorded Record Made During Project Mohole, Phase I Drilling Operation Recording Made During a Trip Out of the Hole Fig. 6 shows a record taken during the Project Mohole, Fig. 5 shows a recording of six variables. This record Phase I drilling operation. Strain gauges mounted on a was made during a trip out of the hole for a bit change. sub in the drill string were used to monitor bending stress A slow recording speed was being used (interval between (upper trace) and torsion (lower trace) in the drill string time signals was 30 seconds). During the recording, the while drilling in I 1,700 ft of water. The distance between pump rate and fluid pressure signals were zero since the each vertical line represents 2.4 seconds. pump was not operating. At the left margin of the record, Bending stress in the drill pipe was caused by the rolling the drilling line was not moving, the rotary rate was zero, motion of the ship. While the bent drill string rotated, the torque was zero and the hook load was zero. At that each particle in the pipe went through a cycle, from zero instant, the slips had just been set prior to removing a to tension to zero to compression, etc. The bending shown stand. Two or three seconds later the stand was removed in Fig. 6 occurred at one point on the pipe during drilling. as shown by the change in the rotary-rate signal (a). The At the left side of the record (zero time), the bending torque increased to a peak value (b) because of the rota­ stress was approximately 2,000 psi. The drilling ship was tion of the table to unscrew the pipe. Next, the empty rolling to one side, thereby bending the pipe. While the elevators were lowered. The only active trace during that ship was rolling to that side, the bending stress during one time was the drilling-line displacement trace (c). Each revolution of the pipe went from 2,000 psi (compression) time the blocks moved 3.6 in., the trace made one cycle, to zero to a maximum tension of 7,000 psi at 1.0 second,

corresponding to one revolution of the wheel engaged with through zero to a maximum compression of 8,000 psi at Downloaded from http://onepetro.org/JPT/article-pdf/15/01/11/2213667/spe-409-pa.pdf by guest on 24 September 2021 the "fast" sheave of the crown block. 2.0 seconds, and back to zero at 2.5 seconds. During the While the empty elevators were lowered, the trace next revolution of the pipe, the ship was approximately at moved through approximately 300 cycles. The trace the center of its roll and the bending stress was low. While appears as one broad line during this period although it the ship was rolling to the opposite side, the pipe was bent is composed of 300 separate lines. A few seconds later in the opposite direction and the stress went from zero at the elevators were latched onto the drill string. During 5.0 seconds through maximum compression, zero, maxi­ this moment, the drilling-line displacement trace was sta­ mum tension, and back to zero at 7.3 seconds. As shown tionary (d). When the drill string was picked up, the by the record, the pipe was turning one revolution in 2.4 hook-load signal increased from zero to a value equal to seconds (25 rpm), and the rolI period of the drilling ship the dynamic load (e). As the drilI string was raised, the was about 10 seconds. hook-load trace remained high. The oscillations in the The torsion signal reflected changes corresponding to the hook-load signal (f) resulted from dynamic forces. During heave (up-and-down movement) of the drilling ship. As the raising of the drill string the drilling-line displacement the ship moved up and down, the opening and closing of signal was erratic because the drill string was decelerated bumper subs apparently caused changes in torsion. As and accelerated while the stand was checked to determine apparent from the trace, the period of the heave of the whether it was empty of mud. After almost a minute and ship was about seven seconds. a half of raising the pipe, the slips were set. At that time, the hook-load signal returned to zero (g). Next, the drill Utilizing the Recording System to Obtain Drill-off Data string was rotated (h) to remove the stand, and the cycle The drill-off procedure for obtaining drilling data was was repeated. During the time of the record in Fig. 5, five initially proposed by Lubinski.' In a drill-off, an entire stands were removed. drilling-rate vs weight-on-bit curve can be obtained over a The sensitivity of some of the recorded signals in Fig. 5 short interval of hole. This decreases the possibility of a was low by choice. During certain test periods, high sensi­ change in formation during the test period. Drilling-rate tivity is desired in one or more variables. The circuitry is vs rotary-rate curves can be obtained by performing a designed so that the sensitivity of any signal can be varied series of drill-offs at several different rotary speeds. over a large range. Description of Drill-Off Method Using the 'Recording Equipment Two curves are needed to obtain a drilling-rate vs weight-on-bit relationship. First, the elongation of the If) If) 6000 drill string as the weight on bit decreases must be deter­ w 0:: mined. (Lubinski's method involved the calculation of this I- If) relationship.) The second element is the variation in weight on bit with time as the bit drills free. If the first curve (!) '"Co z is plotted as displacement vs weight on bit and the second 0 Z as weight on bit vs time, the desired relationship is the w al 6000 product of the slope of the two curves (at each value of weight on bit) plotted vs the weight values. The drill-string elongation can best be obtained by use 1000t---+- of a recording system such as described in this paper. The Z I­ bit is lowered to bottom and the desired maximum weight o LL of the drill-off is applied to the bit. The drill string is then If) I 0 1-----''4-- 0:: al raised until the weight on bit has dropped to zero. During o ..J I- this time a record is made of the displacement of the top of the drill string (from the drilling-rate transducer) and o 2.4 4.8 7.2 9.6 12.0 14.4 16.8 the corresponding hook load. This record permits plotting TIME ( Seconds) drill-string elongation vs weight on bit. Fig. 6-Reeord of hending stress and torsion in drill sIring The change in weight with time as the bit drills off is during Mohole Phase I drjIJing. obtained as follows. The bit is lowered to a point just off

1·\ JOIJRXAL OF PETROLEUM TECH:\,OLOGY bottom, and rotary rate is set at the desired value. The recording system. The formation was a dolomite of fine desired maximum weight is then applied to the bit, the crystalline structure with a few per cent anhydrite and draw-works brake is set and the bit allowed to drill-off. clay, and essentially no porosity. The rock structure was The rotary rate is held constant. Hook load is recorded characteristic of a hanl dolomite. but not as hard as at a constant oscillograph-paper speed. A plot of weight dolomite encountered in deeper zones. The dolomite had on bit vs time can be made from this record. an acoustic velocity in place of approximately 19,000 tt/sec compared to 24,000 ft/sec in typical deeper dolo­ Comparison of Results Obtained with the Method mites. Described and with the Lubinski Method Lubinski' introduced the drill-off method of taking data. Drill-offs were started at 5,020 ft and continued to It represented a considerable improvement over commonly 5,038 ft. The bit used was a new 121/4 -in.':' with 'Ys -in. used procedures. However, the calculation of the drill­ nozzles. The circulation rate was approximately 530 gal! string elongation is subj.ect to two sources of err:Jr. DriIl­ min. The drill-collar string weighed 108,000 Ib in mud collar buckling is neglected, and the exact cross-sectional and was composed of 1,050 ft of 7lj2 - X 3-in. collars. 1 area of the drill pipe ordinarily will not be known because The drill pipe was 5 /2-in., 21.90 Ib/ft. of wear, corrosion and erosion. Effect of Weight on Bit on Drilling Rate The drill string in use during t'ests described later con­ Seven drill-offs were run in the dolomite: tWO at a sisted of 1,050 ft of 7lj2 - X 3-in. drill collars and 3,970 ft rotary rate of 30 rpm, three at 45 rpm and two at 60 of 5lj2 -in. 21.90-lb/ft drill pipe. Measured drill-string rpm. Fig. 8 shows the effect of weight on bit on drilling elongation for the drill-off discussed later was 32.5 in. for rate with a rotary rate of 30 rpm. For simplicity, drilling Downloaded from http://onepetro.org/JPT/article-pdf/15/01/11/2213667/spe-409-pa.pdf by guest on 24 September 2021 a weight change of 90,000 lb. Calculated elongation in the rates at other rotary rates are not shown. However, in each drill pipe for the same weight change, assuming new drill case drilling rate was proportional to weight on bit. pipe with a cross-sectional area of 5.828 sq in., was 24.5 Effect of Rotary Rate on Drilling Rate in. Calculated elongation of the drill collars was I in., for Fig. 9 shows the effect of rotary rate on drilling rate. a total of 25.5 in. In this instance, calculation of the The slope of each of the seven curves of driIling rate vs elongation (based on new pipe) rather than measurement weight on bit is plotted against rotary rate. Fig. 9 indicates would give a 22 per cent error in the values of drilling that, in this dolomite and otherwise under the conditions rate plotted against weight on bit. The drill pipe used of these tests, drilling rate is proportional to rotary rate was old. raised to the 0.6 power. Simulated Drill-Off Record Examination of the curve shows that the point for A simulated drill-off record is shown in Fig. 7. An Drill-off No. 4 is above the curve by a considerable actual drill-off record is not shown because each usually amount. Inspection of the acoustic velocity log for the Dequires several feet of recording paper. At the left side section indicates the reason. The portion of the log of the record in Fig. 7, the bit was on bottom with a cov,ering the total test interval is shown, with the indi­ given weight on bit and the kelly was not moving. The vidual drill-offs indicated, in Fig. 9. DriIl-off No. 4 kelly was lifted (indicated by the driIling-line displacement occurred in an interval which is softer than the other trace slanting from left to right) and the weight on bit intervals with a resultant higher driIling rate. Close exam­ decreased to zero. The kelly was stopped. Each slanted ination of the relative drilling rates at each rotary rate line in the drilling-line displacement trace represents one indicates a close correlation between drilling rate and the revolution of the drilling-rate transducer (3.6 in. of kelly log. For example, DriIl-off No. 1 drilled at a faster rate travel). Therefore, the drill string elongated 14.4 in. when than No.5, as the log indicated it should have. The subjected to this change in weight on bit. The bit was same correlation can b made between Drill-offs No. 2 then run back to bottom (indicated by lines slanting from and No.3. right to left in the drilling-line displacement trace). When the desired weight on bit was obtained, the draw-works brake was locked (no more change in the drilling-line dis­ ':'Hughes OWC-J. placement trace) and weight on bit decreased as the bit 8 drilled free. 7 ;/ Drill-off Data Taken in the San Andres Dolomite 0 with the Electronic Recording System 0 ... 6 0 A series ot drill-offs were made in a Mobil Oil Co. well S in the Magutex field, Andrews County, Tex., utilizing the 5 0 - 0 W TIME SIGNAL I-

0

HOOK LOAD 20,000 40,000 60,000 80,000 100,000 TIME SIGNAL WE IGHT ON BIT (pounds) Fig. 7--Simulated drill-off. Fig. 8-Effect of wei/!:ht on bit on drilling rate.

.IA,"UARY, 1 '5.' 15 1.2 - with an electronic drilling recording system indicates the following. 'J 0 l. A reliable, sensitive drilling recorder is essential to x 1.0 effective research on a drilling rig. I.O 0.6 2. In accurately controlled drill-off tests in San Andres .... (j) W ~ R= r ~0,8 5 dolomite at a depth of about 5,000 ft, drilling rate was ...... :::> 10 ;:: 0 07 proportional to weight on bit and to rotary rate raised 0. to the 0.6 power. UJ I- 0.6 ACOUSTIC VELOCITY LOG I- (J.Lsec 1ft) 3. A new method of taking drill-off data, described in « al this paper, and utilizing the recording system, increases 0:: Z 0 .4 the accuracy of the data considerably in many cases. (!) 0 z I- 4. An acoustic velocity log is valuable for drilling-rate ...J :I: (!) correlations . 0::== UJ 0,2 0 ~ 6!II 55 49 Acknowledgments

0 The authors wish to thank the management of the 0 10 20 30 40 50 60 Research Dept. and the Field Research Laboratory of the ROTARY RATE (rpm) Socony Mobil Co., Inc., for permission to publish this Fig. 9-Effect of rotary rate on drilling rate, Magutex field, paper. We are also indebted to J. D. Wilkinson for assist­ Andrews County, Tex. ance in instrumentation and data analysis, and to personnel Downloaded from http://onepetro.org/JPT/article-pdf/15/01/11/2213667/spe-409-pa.pdf by guest on 24 September 2021 of the Mobil Oil Co. for their assistance in planning and Results of Other Investigators performing field tests. Several attempts have been made to correlate the effect of weight on bit and rotary rate on drilling rate."" The References problem has been attacked theoretically;' 11," through ex­ 1. "Experimental Drilling in Deep Water at La Jolla and Guada· perimentation in the laboratory3-7, 10-12, 14, 16 and by analysis lupe Sites", Publication No. 914, National Research Council of field data!-'4 '(1961) . 2. Lubinski, A.: "Improved Rate·Weight Curve over a Very Theoretical studies have not been adequately translated Short Interval", Oil and Gas Jour. (Nov. 25, 1957) 55, No, to field operations. The laboratory studies are usually de­ 47, 91. signed to specifically minimize the number of variables 3. Simon, R., Cooper, D. E. and Stoneman, M. 1.: "The Funda­ operative and have not as yet led to adequate correlation mentals of Rock Drilling", Paper presented at API Meeting, Columbus, Ohio (April 25, 1956). with field performance. Many reported field tests have 4. Wardroup, W. R., and Cannon, G. E.: "How to Incr.ease Your reduced utility because of changes in formation drilled Drilling Rates", Oil and Gas Jour. (April 30, 1956) 54, No. during the test. 52, 204. 5. Gatlin, c.: "How Rotary Speed and Bit Weight Affect Rotary Effect of Weight on Bit on Drilling Rate Drilling Rate", Oil and Gas Jour. (May 20, 1957) 55, No. Woods and Galle" analyzed AAODC test data taken 20, 193. 6. Speer, J. W.: "A Method for Determining Optimum Drilling in West Texas wells at depths ranging from 6,851 to Techniques", Oil and Gas Jour. (March 31, 1958) 56, No. 13, 12,897 ft. They concluded that drilling rate was pro­ 90; (April 7, 1958) 56, No. 14,148. portional to weight on bit raised to the 1.2 power. Many 7. Moore, P. 1.: "Five Factors That Affect Drilling Rate", Oil formation changes were encountered during these tests, and Gas Jour. (Oct. 6, 1958) 56, No. 40, 141. which made accurate interpretation of the data difficult. 8. Eckel, J, E. and Rowley, D. S.: "How Rotary Speed Affects Penetration", Oil and Gas Jour. (Nov. 25, 1957) 55, No. 47, Inspection of the plotted data, which cover a relatively 86. narrow range of values of weight on bit, indicates that 9. "Back~round Notes on Speed, Weight and Penetration", Pet. more than one curve will fit the data. Eng. (Sept. 1960) 32, No. 10, B-24, Laboratory data of Rowley, et ai," taken at a simulated 10. Cunningham, R. A.: "Laboratory Studies of the Effect of Ro­ tary Speed on Rock-Bit Performance", Paper 851-34-L pre· depth of 3,000 ft in Beekmantown dolomite, also indicate sented at Spring Meeting of the Mid-Continent Dis!., API that drilling rate increases at an increasing rate with 'Div. of Production, Wichita, Kans. (March 30-April 1, 1960). weight on bit. II. Outmans, H. D.: "The Effect of Some Drilling Variables on Later field tests by the AAODC' and field data col­ the Instantaneous Rate of Penetration", Trans. AIME (J960) 219, 137. lected by Speer' agree with our conclusion that drilling 12. Rowley, D. 5., Howe, R. J. and Deily, F. H.: "Laboratory rate is proportional to weight on bit. However, additional Drilling PeI-formance of the Full-Scale Rock Bit", Jour. Pet. accurate drill-off test data are needed to completely estab­ Tech. (Jan., 1961) 13, 71. lish the effects of weight on bit on drilling rate under 13. Woods, H. B. and Galle, E. M.: "Effect of Weight on Pene­ tration Rate", Oil and Gas Jour. (Nov. 25, 1957) 55, No. 47, the many variable down-hole conditions. 88. Effect of Rotary Rate on Drilling Rate 14. Moore, P. 1. and Gatlin, c.: "Six Variable Factors that Affect 8 Penetration Rate", Oil' and Gas Jour. (April 11, 1960) 58, The AAODC ,9 sponsored several field tests in an at­ No. 15, U8. tempt to establish the relationship between drilling rate 15. Graham, J. W. and Muench, N. 1.: "Analytical Determination and rotary rate. Their data indicate that drilling rate is of Optimum Bit Weight and Rotary Speed Combinations", proportional to rotary rate to the 0.7 power in rock that Paper 1349-G presented at 34th Annual Fall Meeting of the SPE, Dallas, Tex. (Oct. 4-7, 1959). drills relatively rapidly. The exponent was reported to be 16. van Lingen, N. H.: "Bottom 'Scavenging-A Major Factor 0.43 in rock that drills relatively slowly. These tests were Governing Penetration Rates at Depth", Jour. Pet. l1ech. run over long intervals of hole. Consequently, the effects (Feb., 1962) 187. of formation changes in the data are very difficult to 17. Galle, E. M. and Woods, H. B.: "How to Find Proper Bit Weight and Rotary Speed", Oil and Gas Jour. (Nov. 14, evaluate. Drill-off data are more reliable because the rela­ 1960) 58, No. 46, 167; (Nov.. 21, 1960) 58, No. 47, 160. tively short hole intervals limit the possibility of formation changes. *** EDITOR'S NOTE: PICTURES AND SKETCHES OF WARREN Conclusions B. BROOKS, JAMES T. DEAN AND WILTON GRAVLEY APPEAR Experience based on four years of research studies ON PAGE 59,

16 JOURNAL OF PETROLEUM TECHNOLOGY